1. Field of the Invention
The present invention relates to an electronic control apparatus used in an electric power steering system for providing an assist force to a steering system of a vehicle by means of the rotational force of an electric motor.
2. Description of the Related Art
In the past, there has been known an electronic control apparatus in which a semiconductor switching element (FET), being a power device, is mounted on a metal substrate, and at the same time, a connecting member for electrically connecting between the metal substrate and parts outside thereof is mounted on the metal substrate.
For example, an electronic control apparatus as described in a first patent document (Japanese patent No. 3644835) includes a metal substrate on which a bridge circuit comprising semiconductor switching elements are mounted for switching a current supplied to an electric motor, a housing with conductive plates, etc., insert molded into an insulating resin and having high current parts mounted thereon, a control board having low current parts such as a microcomputer, etc., mounted thereon, a connecting member for electrically connecting the metal substrate to the housing and the control board, a heat sink being in intimate contact with the metal substrate, and a case being press molded from a metal plate so as to cover the metal substrate, the housing and the control board and mounted on the heat sink.
In the electric control apparatus as described in the above-mentioned first patent document, there arises the following problem. That is, the metal substrate on which the semiconductor switching elements are mounted is needed, and the number of parts required is increased, so the size of the electronic control apparatus is enlarged, and the production cost becomes high.